1. Field of the Invention
This invention relates to the field of aqueous film coating of substrates like pharmaceutical tablets, nutritional supplements, food, confectionery forms, agricultural seeds, and the like, and is specifically concerned with coating substrates with a coating based on polyvinyl alcohol.
2. Description of the Prior Art
The use of the polymer polyvinyl alcohol (PVA) as a film coating has been previously suggested. However, practical usage has been inhibited by the stickiness of grades of the polymer which have rapid solubility in cold water to render them economical to use in current aqueous film coating processes.
Colorcon""s U.S. patent application, Ser. No. 08/466,939 (now U.S. Pat. No. 5,885,617), which is incorporated herein by reference, discloses a moisture barrier film coating composition for forming a moisture barrier film coating for pharmaceutical tablets which comprises polyvinyl alcohol, lecithin, and optionally, a flow aid, and/or a colorant, and/or suspending agent. This coating composition is sold by Colorcon, of West Point, Pa., under the trademark OPADRY AMB.
OPADRY AMB coating compositions produce film coatings having excellent moisture barrier properties. However, due to the inherent tackiness of PVA, the spray rate for coating pharmaceutical tablets in an O""Hara Lab Coat I coater fitted with a 24xe2x80x3 pan containing 12 kilograms of tablets using a aqueous film coating solution/dispersion formed from an OPADRY AMB coating composition is slow (about 25 to 30 grams/minute compared to other types of coating systems which can be sprayed at 50 to 70 grams/min). While a slow spray rate is a disadvantage, such a disadvantage is outweighed by the moisture barrier properties obtained from the OPADRY AMB coating composition, for the special application when a moisture barrier film coating is required to coat a pharmaceutical substrate.
For general purpose use (e.g., where moisture barrier properties are not required), a slow spray rate is not acceptable due to the additional processing costs that are associated with a slow spray rate.
Polyethylene glycol is a known plasticizer used in film coatings to reduce the glass transition temperature of the film forming polymer and to make the polymer less brittle. Inclusion of polyethylene glycol in a coating system would be expected to result in making the coating system more tacky, as predicted by the Williams-Landel-Ferry equation. Accordingly, adding polyethylene glycol to PVA, which is already very tacky, would be expected to result in making the coating system even more tacky, thereby making the problem of tackiness of PVA even worse.
Also, to those skilled in the art, it is well recognized that adding polyethylene glycol to a film coating system generally results in a reduction of the tensile strength of the film coating. A lower tensile strength means a weaker film, which is a drawback.
Also, to those skilled in the art, polyethylene glycol would be expected to compromise the moisture barrier properties of a PVA film coating.
Insoluble materials such as pigments, glidants, and flow aids commonly are used in film coating compositions. For instance, pigment is used to provide a color to the film coating and talc is used as a glidant and a filler to reduce the percentage of the amount of other more costly components in the film coating composition. Use of insoluble materials in the film coating composition may not be haphazard since, as is well recognized by those skilled in the art, adding insoluble materials to a film coating composition typically decreases the tensile strength of the film coating, which means a weaker film is obtained as the amount of insoluble materials in the film coating increases.
Keith et al. U.S. Pat. No. 4,432,965 discloses a sustained release oral dosage form comprising a tablet core containing a pharmaceutically effective amount of quinidine which is coated with a sustained released polymeric coating which contains about 5 to about 20% by weight polyethylene glycol and from about 80 to 95% by weight polyvinyl alcohol. Keith et al. U.S. Pat. No. 4,432,965 discloses that their sustained release coating of PVA and polyethylene glycol dissolves slowly in gastric and intestinal fluids.
It is an object of the invention to provide a coating based on polyvinyl alcohol that has a smooth surface, a shiny gloss, minimal tackiness, good film adhesion, and good tensile strength.
Another object of the invention is to provide a film coating based on polyvinyl alcohol which may be sprayed onto substrates such as pharmaceutical tablets, nutritional supplements, food, confectionery forms, agricultural seeds, and the like at a coating solution spray rate of about 55 to 60 grams per minute. Another object of the invention is to provide a film coating that is fast dissolving.
These and other objects are accomplished by our invention, which is described below.
In accordance with the invention, the inventive dry film coating composition for use in coating pharmaceutical tablet, nutritional supplement, food, confectionery forms, agricultural seed, and the like, comprises 1) polyvinyl alcohol, 2) a plasticizer such as polyethylene glycol or glycerin, and 3) talc.
Preferably, the inventive dry film coating composition includes one or more of the following components: a pigment/opacifier and lecithin.
In accordance with the invention, a method of coating substrates, such as pharmaceutical tablets, nutritional supplements, food, confectionery forms, agricultural seeds, and the like with a film coating, comprises the steps of mixing 1) polyvinyl alcohol, 2) a plasticizer such as polyethylene glycol or glycerin, and 3) talc into water to form an aqueous coating dispersion, applying an effective amount of the coating dispersion onto the substrates to form a film coating on the substrates, and drying the film coating on the substrates. optionally, but preferably, one or more of the following components is/are mixed into water with the polyvinyl alcohol, the plasticizer, and the talc to form the inventive coating dispersion: a pigment/opacifier and lecithin.
The invention also includes the aqueous coating dispersion, the coated substrates, such as coated pharmaceutical tablets, coated nutritional supplements, coated food products, coated confectionery forms, coated agricultural seeds, and the like, and the method of making the dry film coating compositions and the method of making the coating dispersion of the invention.
Polyvinyl alcohol (PVA) is the film former of the coating. The grades of polyvinyl alcohol found useful under the invention correspond to polyvinyl alcohol that comprises partially hydrolyzed polyvinyl acetate which has a percentage of hydrolysis greater than about 86.5 mol. % and preferably in a range of about 86.5 to 89.0 mol. %.
Preferably, the polyvinyl alcohol is micronized to facilitate dissolving the polyvinyl alcohol into the water when forming the aqueous coating solution. Preferrably, the particle size of the micronized polyvinyl alcohol falls in the following quanities and mesh sizes: 47.8% is greater than 200 microns; 28.7% is between 200 and 145 microns; 22.9% is between 145 and 100 microns; 0.5% is between 100 and 80 microns; and 0.1% is between 80 microns.
The polyethylene glycol is a plasticizer for making the coating of the invention non-brittle and non-cracking. Polyethylene glycol having a nominal molecular weight of greater than 1000 has been found useful, and polyethylene glycol having a molecular weight of 3000 is preferred.
Glycerin, another plasticizer, may be substituted for the polyethylene glycol. Unexpectedly, we have found that rather than increasing the tackiness of the film coating as would be expected, glycerin, when used in the inventive coating composition, reduces the tackiness of the resultant film coating by surprisingly acting as a mild detackifier.
The talc is a glidant, and the talc helps improve the smoothness of the final coating since the talc facilitates the tumbling of tablets over one another during coating. Unexpectedly, the talc, in an amount between about 9% and about 45%, and preferably between about 9% and 20%, and more preferably at about 10%, by weight of the coating composition produces an increase in the tensile strength in the film coating, resulting in a stronger film. This is highly unexpected since it would be expected that the tensile strength of a film coating would decrease as the amount of an insoluble component, such as talc, increases in the film coating composition.
The pigment/opacifier may be any food approved colors, opacifiers, or dyes. For example, the pigment/opacifier may be aluminum lakes, iron oxides, titanium dioxide, or natural colors. Examples of such pigments/opacifiers are listed in Colorcon U.S. Pat. No. 4,543,570 issued Sep. 24, 1985 which is incorporated herein by reference.
The lecithin is a detackifier. We have found: 1) the lecithin also acts as a surfactant by helping the wetting of the components of the aqueous coating dispersion; the lecithin helps solvate the polyvinyl alcohol; and the lecithin has a plasticizing effect by locking moisture in the coating so the coating stays flexible and does not become brittle.
The ranges of each component of the dry coating composition of the invention are as follows, by weight:
The following examples illustrate the invention. All units and percentages in the examples are by weight.